On the pteropod pavement of the eastern Rio Grande Rise

Abstract

A pteropod-rich surface layer covers the seafloor on the Rio Grande Rise and its vicinity in less than 3400 m water depth. Sedimentologic analyses of seven box cores, including oxygen isotope stratigraphy and radiocarbon dating, indicate that the pteropod pavement is a lag deposit, and that agitation by bottom currents delays the burial of pteropod shells. Changes in grain size distribution within cores suggest that the strength of bottom circulation has varied considerably through time. Maximum winnowing of fines occurred near the end of full glaciation, decreased in intensity during mid-deglaciation and increased again within the Holocene, culminating in recent erosion. The recent increase in winnowing is probably tied to an increase in the production of North Atlantic Deep Water, which also would have produced a drop in the aragonite compensation depth (ACD). Changes in the abundances of pteropods downcore support this hypothesis. Fe-staining of pteropod shells in the surface layer occurs throughout the Holocene with Fe-accumulation rates on the order of 1 μ m 1000 years .